Question

In my firefox extension I have a sqlite-database with some tables. Using executeAsync(), I updated the tables, inserted some new data and selected some values. The select-case cause me some problems.

Within the handleCompletion()-function I can pass the retrieved data from the table to another function (and can alerting the results, for example). But I would like to pass the result back to the calling function. I searched the net for an answer to my problem, but I can’t find a solution.

What I found:

retrieveData: function() {
    var rows = new Array(); 

    if (this.dbConn.connectionReady){
        statement = this.dbConn.createAsyncStatement("SELECT * " +
                                                "FROM 'domains' " +
                                                ";");

        statement.executeAsync ({
            handleResult: function(aResultSet) {
                var i = 0;

                for (let row = aResultSet.getNextRow(); row; row = aResultSet.getNextRow()) {
                   rows[i] = row;
                   ++i;
                }
            },

            handleError: function(anError) {
                alert("error");
            },

            handleCompletion: function(aReason) { 
                if (aReason != Components.interfaces.mozIStorageStatementCallback.REASON_FINISHED) { 
                    // something went wrong
                    alert("error2");
                } 
            }
        });
    } 

    return rows;
}

This code does not return the expected results. The statement is executed after the method returned the Array “rows”. So, my calling function can never receive the data from the table…

How can I solve this problem? Is there something like a timeout for returning the datarows of the table?

Thanks a lot for help!

Answer 1

You should ideally be dealing in callbacks in the above example. Thats how the SQLite API developers intended the API to be used. 🙂

retrieveData: function(_callback) {
   ...
   statement.executeAsync ({
      ...
      handleCompletion: function(aReason) { 
         ...
         _callback(rows);
      }
   });
}

And where you call the function:

retrieveData(function(rows) {
   // do stuff with rows here
});